A fan motor of an air conditioner in a vehicle is driven by a controller so that the magnitude of a stream of air which is sent into a room of a vehicle can be adjusted in several steps from a weak stream of air to a powerful stream of air. The adjustment of the magnitude can be manually made by using a fan switch such as a rotary switch. However, when the air conditioner is operated in a heating mode and the fan switch has been switched, the controller drives the electric fan through the fan motor to send out a powerful stream of air into the room of the vehicle. Then, if a temperature of the outside air of the vehicle falls down to a cold temperature, the cold outside air is drawn into the room of the vehicle by operation of the electric fan together with warm air from a heater.
Consequently, a temperature in the room is reduced and a desired room temperature can not be obtained. Therefore, in order to obtain the desired room temperature in that condition, it is necessary to manually operate the fan switch so that the controller drives the fan through the fan motor to send out a weak stream of air into the room. Such a manual operation of the switch is troublesome.